Methods, mobile devices and data management systems of the type cited at the outset are fundamentally known. Communication modules for wireless communication, that is to say for sending and/or receiving data, for example information data, control data, authorization data, identification data or the like, are fundamentally known. The operation of such communication modules requires electric power, which is usually provided by replaceable or rechargeable energy stores. Frequently, the energy stores are configured as primary cells, but sometimes also as secondary cells. In particular, it is known practice to configure such energy stores as buffer batteries. The running time of these energy stores is finite and, in particular, dependent on the operation of the communication module. After the running time has expired, the energy store needs to be charged or replaced. In a system in which a multiplicity of corresponding communication modules are used, for example in a data management system that comprises multiple mobile handheld machine tools and/or user identification units, maintaining and/or changing the energy stores represents a disadvantageous expenditure in terms of time and cost.